The subject matter of this invention is related to the subject matters of inventions entitled "Switch Components and Multiple Data Rate Non-Blocking Switch Network Utilizing the Same" (issued as U.S. Pat. No. 4,914,429), "Virtual Tributary Cross Connect Switch and Switch Matrix Utilizing the Same" U.S. Ser. No. 07/283,178, and "System for Cross-connecting High Speed SONET Digital Signals" U.S. Ser. No. 07/283,172, all of which filed of even date, assigned to the assignee hereof, and all of which are hereby incorporated by reference herein.
This invention relates generally to cross-connect systems for cross-connecting high speed digital signals. The invention more particularly relates to a modular, non-blocking, expandable, digital cross-connect system capable of cross-connecting high-rate digital signals such as DS-3 and SONET and lower-rate signals such as DS-1, CEPT32, etc., where the lower-rate signals may be component of the high-rate signals, or may terminate on low speed lines.
The telecommunication network servicing the United States and the rest of the world is presently evolving from analog transmission to digital transmission with ever-increasing bandwidth requirements. Fiber optic cable has proved to be a valuable tool of such evolution, replacing copper cable in nearly every application from large trunks to subscriber distribution plants. Fiber optic cable is capable of carrying much more information than copper with lower attenuation.
While fiber optic cable represents the future in telecommunications, presently there remains an entire telecommunication network comprised of various cable types, served by equipment of different vintages, and run according to various coexisting transmission standards. While older standards, cables, and equipment will be eventually phased out, for the time being it is necessary that all the old and new standards, equipment and transmission lines be as compatible as possible. For example, in a wire plant, every signal should be connectable to every other signal. To achieve this, it is not enough to simply multiplex signals from lower to high orders and vice-versa. In addition to a mux/demux/ function, signal format conversion operations must be performed before connectibility can be achieved. For instance, a DS-3 signal cannot simply be connected to an STS-1 signal as these signals are at different rates and use different multiplexing formats.
The present devices for cross-connection and switching require rate and format conversion means and are typically incapable of passing the bandwidth which fiber optic cables can carry. Where wideband switching is attempted, the utilized devices are often not compatible with each other as they typically employ proprietary signaling schemes. Furthermore, the equipment conducting the wideband switching is typically limited in its range of sizes and features, thereby making network expansion difficult and costly.
In attempting to accommodate the protocols, equipment, and cables of the past while providing for the direction of the feature, various standards and system requirements relating to fiber optic cables have been adapted. In particular, the T1 Standards Committees of ANSI have provided a draft document ANSI T1.105-1988 dated Mar. 10, 1988 which sets forth specifications for a rate and format of signals which are to be used in optical interfaces. Additional details and requirements are set forth in Technical Advisory publications SR-TSY-000202, --000233, -000253, -000303 Issue 3 of Bell Communication Research (BellCore). The provided specifications detail the SONET (synchronous optical network) standard. SONET defines a hierarchy of multiplexing levels and standard protocols which allow efficient use of the wide bandwidth of fiber optic cable, while providing a means to merge lower level DS0 and DS1 signals in a common medium. In essence, SONET establishes a uniform, standardized transmission and signaling scheme which provides a synchronous transmission format that is compatible with all current and anticipated signal hierarchies. Because of the nature of fiber optics, expansion of bandwidth is easily accomplished.
While the SONET specifications provide standards which in theory permit cross-connection of high-rate digital carrier signals with other high-rate digital carrier signals (e.g. DS-3 and SONET), lower-rate digital signals with other lower-rate signals both carried by the high-rate signals (e.g. DS-2, DS-1, CEPT32, DS-0), and lower-rate signals carried by high-rate signals with lower-rate signals carried on lower-rate digital carriers (e.g. add-drop a DS-1 from a SONET or DS-3 carrier), systems for accomplishing the same are not known in the art. Clearly, then such systems are needed.